Respiration-induced patient motion has become a major obstacle for achieving high-precision radiotherapy of cancers especially in the thorax and upper abdomen. As the target is continuously moving, an additional margin has to be added to the clinical target volume to compensate for the uncertainty in the tumor and organ motion, causing toxicity to the normal tissue and limiting the dose delivered to the target. To account for the tumor motion, surrogate tracking methods are commonly used in clinics during radiotherapy. However, the relationship between the surrogate and tumor motion is hard to generalize as it depends on individual patients, tumor location, treatment fractions, and sometimes shows complex patterns or transient, unpredictable changes. Hence, there is an urgent need to better scrutinize the current surrogate-based motion management strategies. Moreover, the most robust motion management strategy for the given patient should be determined in the pre-treatment setting but the investigators currently lack a sufficient tool to provide this information.